3'.3> 

Issued  January  17,  19H. 

HAWAII  AGRICULTURAL  EXPERIMENT  STATION, 

E.  V.  WILCOX,  Special  Agent  in  Charge. 


Bulletin   No.  31. 


RICE  SOILS.  OF  HAWAII 


THEIR  FERTILIZATION  AND  MANAGEMENT. 


BY 


W.  P.  KELLEY, 


CHEMIST. 


UNDER  THE  SUPERVISION  OF'"*— ^_ 
OFFICE  OF  EXPERIMENT  STATIONS, 

U.  8.  DEPARTMENT   OF   AGRICULTURE. 


ORY 


s^spr 


WASHINGTON: 

GOVERNMENT  PRINTING  OFFICE. 

1914. 


HAWAII  AGRICULTURAL  EXPERIMENT  STATION,  HONOLULU. 

[Under  the  supervision  of  A.  C.  True,  Director  cf  the  Office  of  Experiment  Sta- 
tions, United  States  Department  of  Agriculture.] 

Walter  H.  Evans,  Chief  of  Division  of  Insular  Stations,  Office  of  Experiment 

Stations. 

STATION  STAFF. 

E.  V.  Wilcox,  Special  Agent  in  Charge, 
J.  Edgar  Higgins,  Horticulturist. 
W.  P.  Kelley,  Chemist. 

C.  K.  McClelland,  Agronomist. 

D.  T.  Fullaway,  Entomologist. 

W.  T.  McGeorge,  Assistant  Chemist. 
Alice  R.  Thompson,  Assistant  Chemist, 
C.  J.  Hunn,  Assistant  Horticulturist. 
V.  S.  Holt,  Assistant  in  Horticulture, 
C.  A.  Sahr,  Assistant  in  Agronomy, 


I8SU  .7.  1914. 

HAWAII  AGRICULTURAL  EXPERIMENT  STATION, 

E.  V.  WILCOX,  Special  Agent   in  Charge. 


Bulletin    No.   31. 


RICE  SOILS  OF  HAWAII 

THEIR  FERTILIZATION  AND  MANAGEMENT. 


BY 

W.  P.  KELLET 


5 
CHEMIST. 


UNDER   THE  SUPERVISION'  OF 

OFFICE  OF  EXPERIMENT  STATIONS, 

U.  B.   DEPARTMENT   OF    AGRICULTURE. 


WASHINGTON: 
GOVERNMENT   PRINTING   OFFICE. 

1014. 


LETTER  OF  TRANSMITTAL 


Honolulu,  Hawaii,  October  1,  1913. 
Sir:  I  have  the  honor  to  submit  herewith  and  recommend  for  publication,  as 
Bulletin  No.  31  of  the  Hawaii  Agricultural  Experiment  Station,  a  paper  on  Rice 
Soils  of  Hawaii :  Their  Fertilization  and  Management,  by  W.  P.  Kelley,  chemist. 
The  experiments  on  rice  as  carried  out  by  this  station  indicate  quite  conclusively 
that  for  the  most  successful  production  of  rice  all  conditions  which  tend  toward 
nitrification  should  be  avoided.  The  application  of  nitrates  has  been  found  to 
be  of  little  or  no  avail,  and  sometimes  even  positively  injurious,  while  the  use 
of  ammonium  sulphate  brings  about  greatly  increased  yields.  In  harmony  with 
this  finding  is  the  evidence  that  conditions  which  allow  nitrification  to  take 
place  in  rice  soils  result  in  a  diminished  yield  of  rice.  It  appears,  therefore, 
that  ammonium  sulphate  should  be  the  form  of  commercial  nitrogen  to  apply 
to  rice  and  that  rice  soils  should  not  be  aerated  between  crops.  These  results 
are  probably  applicable  to  other  regions  than  the  rice  lands  of  Hawaii. 
Respectfully, 

E.  V.  Wilcox, 

Special  Agent  in  Charge. 
Dr.  A.  C.  True, 

Director  Office  of  Experiment  Stations, 

U.  S.  Department  of  Agriculture,  Washington,  D.  C. 

Publication  recommended. 
A.  C.  True,  Director, 

Publication  authorized. 
D.  F.  Houston, 

Secretary  of  Agriculture, 


CONTENTS 


Page. 

Introduction 5 

Origin  or  rice  soils 0 

Mechanical  composition ' . 6 

Chemical  composition 8 

Fertilizer  experiments 10 

The  form  of  nitrogen  for  rice 17 

Ammonification  and  nitrification  in  rice  soils 20 

The  management  of  rice  soils 22 

Summary 24 

(2) 


RICE  SOILS  OF  HAWAII:  THEIR  FERTILIZATION 
AND  MANAGEMENT. 


INTRODUCTION. 

The  extensive  soil  investigations  that  have  been  made  up  to  the 
present  time  have  dealt  principally  with  dry  lands,  in  which  the 
moisture  and  other  conditions  differ  greatly  from  those  prevailing  in 
rice  soils.  In  America  in  particular  very  little  study  has  been  devoted 
to  submerged  lands,  and  little,  indeed,  is  really  known  about  them. 
Consequently  recommendations  for  the  treatment  and  management 
of  rice  soils  are  generally  based  on  knowledge  gained  from  experience 
with  dry  lands.  It  is  evident,  however,  that  conclusions  applicable 
to  dry  soils  do  not  necessarily  apply  to  submerged  soils  such  as  are 
used  in  rice  culture,  and,  in  fact,  it  is  well  known  in  oriental  countries 
that  rice  lands  demand  different  treatment  from  those  devoted  to 
dry-land  cultures. 

The  one  condition  that  is  most  obviously  different  in  rice  soils  and 
dry  lands  is  that  of  aeration.  The  fact  that  aeration  is  essential  to 
the  successful  growth" of  most  crops,  and  the  belief  that  fertility  is  in 
some  way  dependent  upon  its  maintenance,  has  caused  agriculturists 
to  recommend  for  rice  soils  practices  designed  to  secure  aeration  in 
the  belief  that  this  is  as  essential  for  successful  rice  culture  as  for 
culture  of  other  crops.  Experiments  are  not  wanting,  however, 
which  show  this  to  be  untrue. 

One  of  the  most  important  matters  affecting  the  culture  of  rice  is 
the  form  in  which  nitrogen  is  taken  up  by  the  crop.  It  is  well  known 
that  the  degree  of  aeration  in  soils  determines  very  largely  the  form 
assumed  by  available  nitrogen.  This  phase  of  the  subject  has  been 
reported  upon  previous!}7  by  the  writer,1  but  will  be  further  empha- 
sized in  this  bulletin  on  account  of  the  principle  involved  and  the 
practical  importance  attached  to  it. 

In  connection  with  the  general  soil  investigations,  which  have  been 
under  way  in  the  laboratory  of  the  Hawaii  station  for  several  years, 
the  rice  lands  of  the  Hawaiian  Islands  have  received  considerable 
attention.    For  a  Dumber  of  years  also  ii<'l<l  experiments  with  different 

i  Hawaii  Sta.  Bui.  24. 
(3) 


fertilizers  for  rice  have  been  conducted  by  the  station.  The  subject 
has  been  approached  from  a  number  of  standpoints,  both  practical 
and  scientific,  and  it  is  believed  the  results  are  of  sufficient  interest 
and  value  to  warrant  publication  at  this  time. 

ORIGIN  OF  RICE  SOILS. 

The  rice  soils  of  Hawaii  are  located  at  or  near  sea  level  along  the 
coast  and  are  not  extensive  in  area,  amounting  to  about  10,000  acres, 
and  during  recent  years  the  tendency  has  been  to  plant  other  crops 
on  some  of  the  lands  hitherto  devoted  to  rice  because  of  low  yields, 
labor  difficulties,  etc.  The  extent  of  the  industry,  therefore,  is  on  the 
decline.  The  soils  have  their  primary  origin  in  basaltic  lavas,  just 
as  is  the  case  with  all  the  soils  of  the  islands,  but  in  addition  they 
frequently  contain  varying  amounts  of  coral  lime  (CaC03),  which 
has  become  thoroughly  mixed  with  the  lava  residues.  Whether  or 
not  the  coral  is  visible  on  the  surface,  in  practically  all  cases  the  rice 
lands  are  underlain  at  various  depths  with  deep  beds  of  coral  lime- 
stone. Notwithstanding  the  fact  that  the  lavas  are  typical  basalts,  the 
chemical  and  physical  properties  vary  enormously;  moreover,  the 
rates  of  disintegration  and  the  composition  of  the  residuum  differ 
greatly  from  place  to  place.  Therefore  the  soils  coining  from  lavas 
of  essentially  the  same  type  may  be  very  different  in  composition 
and  properties.  The  .low  lands  in  and  around  Honolulu,  for  instance, 
having  been  derived  from  the  disintegration  of  volcanic  cinder, 
typical  black  sands,  are  widely  different  from  the  rice  lands  on  the 
leeward  side  of  Oahu,  both  in  chemical  and  physical  properties.  This 
is  especially  noticeable  in  the  relative  percentages  of  lime  and 
magnesia. 

In  most  instances  the  rice  soils  are  strictly  alluvial,  although  on 
account  of  the  close  proximity  of  the  mountains  there  has  been  but  a 
limited  transportation  of  the  soil  materials.  The  soils  in  places 
contain  a  high  percentage  of  organic  matter. 

In  certain  localities,  as,  for  instance,  the  Hanalei  Valley,  on  Kauai, 
the  soils  contain  high  percentages  of  clay  and  are  of  a  close  texture. 
The  rice  lands  around  Honolulu,  on  the  other  hand,  contain  quantities 
of  sand  and  gravel  unusual  for  Hawaiian  soils,  and  as  a  consequence 
are  open  and  porous.  Samples  of  soil  from  all  the  important  rice  sec- 
tions have  been  examined. 

MECHANICAL  COMPOSITION. 

In  view  of  its  bearing  on  irrigation,  etc.,  the  mechanical  composi- 
tion as  shown  by  physical  analysis  has  been  determined  and  is  re- 
corded in  the  following  on  page  5. 


Physical  analyses  of  rice  soils. 


District. 

Fine 
gravel, 

2  1  nun. 

Coarse 

saint. 
1  0.2 
nun. 

Fine  sand 

0.2  0.04 

mm. 

Silt. 
0.04-0.01 

nun. 

Fine  silt . 

0.01-0.002 

nun. 

Clay, 
0.002  mm. 

Or  less. 

Organic 

matter 

and 

combined 

water 

Waikiki: 

Soil  298 

Ptr  c<  n(. 
20.91 
18.61 

1.15 

1.02 
.  82 

.35 
.33 
.13 

.06 

.05 
.22 

.15 
.46 

.41 
.22 

1'ti  cent. 
18.75 
18.30 

1.61 
1.28 
1.63 

.69 
.86 
.22 
.31 

.19 

.11 

3.09 
3.59 

.83 

.  64 

Per  cent. 
22.04 

22.  74 

18.34 
20.  63 
15.33 

18.78 
18.60 
18.13 
16.75 

16.03 
15.29 

25.94 

34.44 

21.49 
11.29 

Pi  r  a  nt. 
8.69 
8.10 

16.28 

17.  sS 
15.77 

13.57 
15.97 
20.42 
19.27 

30.79 
28.94 

20.97 
19.30 

27.45 
15.27 

12.  11 

13.  18 

23.88 
22.11 

21.73 

22.92 
21.97 
22.37 

23.  42 

14.64 
20.67 

15.96 
10.96 

7.61 
20.07 

Per  cait. 

7.23 
9.52 

25.39 
24.06 
31.61 

25.70 
23. 97 
19.19 
22.98 

20.16 
21.73 

19.84 
14.29 

6.38 
6.19 

Per'cerU. 

s.71 

Subsoil  293 

10.77 

Fort  Shatter: 

Soil  332.              

14.37 

Subsoil  333 

14.t).'. 

Soil  334 

15.23 

Kailua: 

Soil  337 

18.72 

Subsoil 338.   ... 

19.54 

Soil  339 

21.17 

Subsoil  340 

19.41 

Kaneoho: 

Soil  343 

15.44 

Subsoil  344 

13.20 

Waiaholo: 

Soil  345 

15.04 

Subsoil  34f> 

15.31 

Kalaunui: 

Soil  347 

36.14 

Subsoil  34S 

49.24 

The  above  data  show  that  the  rice  soils  of  Oahu.  with  the  ex- 
ception of  those  from  the  Waikiki  and  Kalaunui  districts,  are  very 
similar  in  mechanical  composition,  and  are  made  up  of  approxi- 
mately equal  quantities  of  fine  sand,  silt,  fine  silt,  and  clay.  The 
Waikiki  soils,  on  the  other  hand,  contain  relatively  small  amounts 
of  clay,  with  correspondingly  larger  amounts  of  the  coarser  grained 
particles.  None  of  tHe  soils  except  from  this  district  contains  any 
material  coarser  than  fine  gravel,  while  that  from  Waikiki  contains 
several  per  cent  of  stones,  etc.  This  point  is  of  importance  because 
of  its  bearing  on  tillage  and  drainage:  The  soils  from  Kalaunui, 
on  the  other  hand,  are  very  highly  organic,  and  in  places  this  land  is 
peaty  to  a  considerable  degree.  The  organic  matter  of  this  soil,  how- 
ever, retards  the  passage  of  water  through  it,  with  the  result  tr^at  the 
amounts  of  water  used  in  its  irrigation  are  practically  normal  for 
the  islands. 

In  the  main  these  soils  are  to  be  classified  as  clay  loams  with  a 
rather  high  organic  content.  The  irrigation  of  all  these  soils  requires 
relatively  large  amounts  of  water  on  account  of  their  porous  nature. 

In  considering  the  mechanical  composition  cf  Hawaiian  soils  it 
should  be  especially  borne  in  mind  that  the  terms  clay,  fine  silt,  etc., 
have  reference  only  to  the  size  of  the  particles,  and  that  these  art- 
made  up  of  different  chemical  substances  from  those  that  go  to 
make  up  clay  in  most  continental  soils.  Furthermore,  the  prop- 
erties of  so-called  clay  in  Hawaiian  -oils  differ  from  the  properties 
of  other  flay-.  It  i-  not  composed  primarily  of  kaolin,  but  is  made 
up  of  ferric  and  aluminum  hydrates,  together  with  double  silicates 
of  iron   and   aluminum   and   perhaps   some   aluminum   silicate.     In 


addition  the  coarser  particles  are  in  the  main  merely  lava  fragments 
on  their  way  toward  more  complete  disintegration.  These  frequently 
show  under  the  microscope  the  characteristic  structure  of  lava.  As 
time  goes  on  the  relative  proportions  of  these  constituents  will 
change,  so  that  eventually  a  higher  percentage  of  clay  and  fine  silt 
will  predominate.  The  upland  soils  at  the  present  time  frequently 
contain  practically  no  material  coarser  than  silt,  with  abnormally 
large  quantities  of  clay.  The  soils  are  typical  laterites,1  and  in 
interpreting  the  analytical  results  reported  herein  it  is  important 
to  bear  this  in  mind. 

CHEMICAL    COMPOSITION. 

The  chemical  composition  of  these  soils,  as  determined  by  the  use 
of  the  official  methods,  is  shown  in  the  following  table: 

Chemical  composition  of  rice  soils. 


District. 


Insoluble 

Potash 

Soda 

Lime 

Magnesia 
(MgO). 

matter. 

(KsO). 

(Na20). 

(CaO). 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

Per  cent. 

41.69 

0.42 

1.47 

1.99 

9.42 

38.82 

.47 

1.36 

2.48 

9.75 

44.57 

.25 

.46 

.97 

.94 

45.75 

.26 

.36 

.87 

.58 

44.94 

.27 

.34 

.81 

.99 

40.53 

.26 

.45 

.76 

.82 

42.  60 

.16 

.46 

.59 

.49 

37.20 

.14 

.44 

.43 

.26 

38.20 

.06 

.37 

.47 

.31 

50.10 

.10 

.36 

1.22 

.87 

51.15 

.15 

.38 

1.65 

.73 

50.52 

.09 

.24 

1.20 

1.08 

48.30 

.08 

.28 

1.63 

1.54 

37.  82 

.12 

.31 

2.20 

.79 

27.70 

.09 

.32 

2.76 

.78 

42.40 

.16 

.10 

1.16 

2.67 

40.40 

.27 

.10 

.97 

3.35 

47.25 

.19 

.41 

1.18 

2.28 

47.00 

.17 

.34 

.97 

6.98 

45.18 

.15 

.42 

1.26 

1.72 

45.  70 

.14 

.45 

1.38 

2.65 

45.35 

.15 

.  29 

.96 

4.16 

43.30 

.17 

.34 

1.16 

3.07 

Manga- 
nese oxid 
(Mn304). 


Ferric 

oxid 

(F203). 


OAHU. 

Waikiki: 

Soil  292 

Subsoil  293 

Fort  Shafter: 

Soil  332 

Subsoil  333 

Soil  334 

Kailua: 

Soil  337 

Subsoil  338 

Soil  339 

Subsoil  340 

Kaneohe: 

Soil  343 

Subsoil  344 

Waiahole: 

Soil  345 

Subsoil  346 

Kalaunui: 

Soil  347 

SubSbil348.... 

KAUAI 

Hanalei  Valley: 

Soil  460 

Soil  461 

Soil  462 

Soil  463 

Soil  464 

Soil  465 

Soil  466 

Soil  407 


Per  cent. 

0.27 

.21 

.32 
.30 
.13 

.09 

.27 


.32 
.35 


.09 
1.16 
.02 
.04 
.14 
.23 
.15 
.13 


Per  cent. 
18.01 
21.22 

18.84 
18.48 
17.56 

19.01 
19.67 
24.80 
26.15 

11.20 
10.50 

17.25 
16.18 

7.05 
6.44 


16.22 
17.10 
14.82 

18.20 
15. 32 
15.23 
18.16 
15.91 


1  The  decomposition  of  basaltic  lavas  usually  gives  rise  to  soils  high  in  iron  and 
aluminum  and  relatively  low  in  silica,  and  while  the  most  finely  divided  particles  are 
usually  referred  to  as  clay,  the  name  is  improperly  applied.  Recently  Ulpiani  (Staz. 
Sper.  Agr.  Ital.,  45  (1912)  pp.  629-653)  suggested  that  this  process  be  called  lateritization 
in  contradistinction  to  kaolinization,  which  takes  place  in  the  decomposition  of  orthoclase 
feldspars. 


Chemical  composition  of  rice  soils — Continued. 


District. 

Alumina 

(AlsO,). 

Phos- 

phorio 

acid 

(PsO»). 

Sulphur 
trioxid 
(SO,). 

Titanic 
dioxid 
(TiO,). 

Los-;  on 
ignition. 

OAHU. 

:ki: 
Sail  292 

Per  cent. 
14.10 
13.09 

17.10 
17.42 

19.35 

14.94 
14.50 

12. :.' 

12.  45 

20.  35 
20.90 

14.92 
15.  30 

14.40 
12.42 

20.  15 
20.10 
19.12 
13.60 
20.30 
19.95 
16.95 
20.35 

Percent. 

o.  as 

.71 

.32 
.26 
.45 

.76 
.68 
.29 
.22 

.20 
.23 

.21 
.23 

.19 
.13 

.44 
.52 
.53 
.35 
.51 
.  72 
.31 
.56 

Percent. 

0.0S 

.11 

.03 
.10 
.23 

.26 
.26 
.20 
.20 

.04 
.04 

.20 
.13 

.31 
.80 

.27 
.28 
.35 
.30 
.28 
.31 
.26 
.21 

Per  cent. 
2.17 
2.64 

2.26 
2.  17 

1 .  53 

2.  43 
2. 1  : 
2.  92 
2.81 

2.24 

2.  37 

1.64 
1.60 

2.28 
1.90 

2.78 

3.00 
2.67 
2.06 
2.93 

2.27 
2.57 
2.70 

Percent 
9.10 
9.  92 

13.96 
13.58 
13.70 

18.63 
18.43 
21.10 
18.41 

13.85 

12.  30 

13.  22 
14.70 

34.52 
46.70 

14.15 
14.35 

12. 25 
10.42 

12.  95 
11.27 
11.80 

13.  35 

Per  cent. 
100.  78 

100.02 

100. 13 
100.32 

98.94 
100.24 
100.58 

99.76 

100.94 
100.92 

100.99 
100.42 

100.31 
100.39 

100.59 
101.60 
101.07 

100.  43 
101.17 
100.30 
101.10 

101.  35 

Ptr  cent. 

(>.  HI 

Subsoil  293 

.16 

Fort  Shaffer: 

-        :     m 

.  It; 

-oil  333 

.  13 

Soil  334 

Kailua: 

.  23 

.44 



Subsoil  33S 

.  42 

Soil  339 

.41 

Subsoil  340 

.30 

Kaneohe: 

Soil  313 

.20 

Subsoil  344 

.  17 

Waiahole: 

Soil  345 

.21 

Sub-oil  346 

.20 

Kalaunui: 

Soil  347 

1.24 

Subsoil  348 

1.44 

KAUAI. 

Hanalei  Vallev: 

Soil  460..." 

.26 

Soil  461 

.24 

Soil  462 

.20 

Soil  463 

.  Is 

Soil  464 

.20 

Soil  465 

.15 

Soil  466 

.17 

Soil  467 

.17 

It  will  at  once  be  seen  that  these  soils  differ  from  normal  soils  not 
only  in  physical  properties  but  also  in  chemical  composition. 

The  lavas  from  which  these  soils  have  been  derived  are  made  up 
primarily  of  pyroxenes  or  amphiboles  and  soda-lime  feldspars,  and 
therefore  are  characteristically  basic.  In  the  disintegration  process 
solution  and  oxidation  play  the  most  important  part-,  with  the  result 
that  the  soils  formed  contain  iron  and  aluminum  in  great  quantities, 
while  the  potash,  soda,  lime,  and  magnesia  are  largely  leached 
out  as  silicates.  In  a  few  instances  the  rice  soils,  however,  contain 
relatively  large  amounts  of  lime  and  magnesia,  due  partly  to  admix- 
tures with  coral  limestone  and  in  part  to  the  type  of  lava  from  which 
they  were  derived.  It  is  also  noteworthy  that  the  ratio  of  lime  to 
magnesia  in  these  soils  is  abnormal,  the  latter  sometimes  being  pres- 
ent in  great  excess  above  the  former.  In  view  of  the  interest  now 
taken  in  the  lime-magnesia  ratio  the  relations  of  these  tw<  elements 
are  of  special  interest,  particularly  since  rice  has  been  extensively 
studied  in  connection  with  this  ratio. 

The  potash  content  is  rather  low,  while  phosphoric  acid  us  generally 
present  in  large  amounts.  From  a  superficial  examination  of  these 
analyses  it  would  seem  that  potash  fertilization  is  needed.  It  will  be 
shown  in  connection  with  the  fertilizatic  n  studies,  however,  that  there 


8 

is  no  need  for  potash  fertilizer.  The  decomposition  of  the  lava  frag- 
ments is  greatly  increased  by  the  products  arising  from  the  decay  of 
organic  matter  under  the  prevailing  anaerobic  conditions,  with  the 
result  that  potash  is  rendered  soluble  at  a  rate  sufficient  to  supply  the 
needs  of  rice,  but  the  limited  supply  of  potash  present,  together  with 
the  fact  that  large  amounts  of  potash  are  taken  up  by  rice,  will  sooner 
or  later  necessitate  the  use  of  potash-bearing  fertilizer. 

FERTILIZER    EXPERIMENTS. 

Some  fertilizer  experiments  with  rice  have  already  been  published 
by  this  station.1  The  results  were  such  as  to  emphasize  the  need  for 
a  more  systematic  study  of  this  question,  and  in  view  of  the  fact  that 
the  yields  obtained  by  the  rice  growers  throughout  the  islands  are 
frequently  unprofitable,  a  series  of  fertilizer  tests  were  instituted  on 
the  rice  trial  grounds  of  the  station  in  the  spring  of  1909.  These  ex- 
periments were  continued  on  the  same  plats  throughout  seven  con- 
secutive crops.  In  Hawaii  little  or  no  rotation  of  crops  is  practiced, 
and  two  crops  of  rice  are  grown  on  the  same  land  each  year. 

The  soil  on  which  these  experiments  were  made  had  been  previ- 
ously devoted  to  rice  culture  and  was  known  to  be  quite  uniform  in 
productivity.  After  the  plats  had  been  laid  out.  however,  an  addi- 
tional crop,  without  fertilization,  was  grown  for  the  purpose  of 
determining  more  definitely  their  uniformity.  The  results  showed 
the  plats  to  be  extremely  uniform  throughout,  practically  the  same 
yield  having  been  obtained  from  each.  The  plats  were  separated  by 
low  dikes  so  constructed  as  to  prevent  the  lateral  movement  of  fer- 
tilizers and  irrigation  was  adjusted  so  as  to  insure  a  constant  water 
supply  of  about  2  inches  in  depth  above  the  surface  of  the  soil. 

After  harvesting  the  first  crop  the  original  plats  were  divided  into 
two  equal  portions,  which  here  are  to  be  designated  as  series  A  and  B. 
The  former  were  fertilized  previous  to  the  time  of  transplanting  the 
spring  crop  only,  while  the  latter  received  the  same  applications  in 
like  quantities  to  both  the  spring  and  fall  crops.  Previous  experience 
had  suggested  that  nitrogen  would  prove  to  be  the  most  needed  ele- 
ment, and  this  was  borne  out  by  the  results  obtained  later.  The  yields 
obtained,  fertilizers  applied,  etc..  are  recorded  in  the  tables,  using 
the  following  values  in  calculating  the  cost  of  fertilizers,  profits,  etc. : 
Ammonium  sulphate,  $80  per  ton;  superphosphate,  $20  per  ton: 
potassium  sulphate,  $55  per  ton;  paddy,  $0,025  per  pound.  In  calcu- 
lating the  profit'or  loss,  the  extra  expense  incurred  from  the  increased 
labor  attached  to  making  the  application  of  fertilizers,  harvesting, 
and  marketing  the  increased  yields,  etc.,  was  not  included. 

1  Hawaii  Sta.  ttpts.  1907  and  1908. 


9 

Results  of   applying  fertiliser*    to   spting   crop   only. 
1909— SERIEi  A. 


Plat. 


rertUUer. 


10 


None 

Superphosphate,  225  pounds: 
Potassium  sulphate,  120 
pounds 

Ammonium  sulphate,  150 
pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  150 
pounds;      superphosphate, 

225  pounds 

:  None 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  300 
pounds;  superphosphate, 
450  pounds;  potassium  sul- 
phate, 240  pounds 

Ammonium  sulphate,  300 
pounds 

Ammonium  sulphate,  150 
pounds 

None 


Yield  per  acre. 


Spring  crop. 


Straw. 


Lbs. 
1,300 


1,641 
1,722 


2,112 
1,267 


,950 


2,762 
2,405 


1,950 
1,379 


Fall  crop. 


Paddy 


Lbs. 
1,462 


1,625 
2,007 


2,128 
1,543 


2,242 

2,957 

2,730 

2,285 
1,528 


Straw. 


Lbs. 
1,950 


2,242 

2,667 


2,275 
2,275 


2,925 

2,250 

2,307 

2,502 
2,372 


Paddy 


Lbs. 
U.950 


3,250 
2,632 


3,217 
3,347 


3,347 


3,152 
3,315 


3,867 
3,315 


ln- 


(  oat 


Total     crease     0.f.ft"r 


yield 
per  an- 
num. 


I.te.        Lbs 


in 
paddy 
per  an- 
num. 


tilizer. 


8,758 
9,028 


9,732 
8,432 


10,464 

11, 121 

10,757 

10,604 
8,594 


9 

0 

479 


723 

1,243 
1,179 
1,286 


Profit 
(+)or 

loss 
(-)per 
an- 
num. 


$5.55 
9.30 
S.25 


I  -15.33 

-  9.30 

j  +  3.72 


11.55 

23.10 
12.00 
6.00 


+  6.52 

+  7.96 

+  17.47 
+26.15 


1910— SERIES  A. 


None 

Superphosphate,  225  pounds; 
potassium  sulphate,  120 
pounds 

Ammonium  sulphate,  150 
pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds 

None 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  300 
pounds;  superphosphate, 
450  pounds;  potassium  sul- 
phate, 240  pounds 

Ammonium  sulphate,  3U0 
pounds 

Ammonium  sulphate,  150 
pounds 

None 


1,657 

1,527 

1,560 

1,690 

1,722 

1,852 

1,950 

1,722 

1,560 

1,982 
1,690 

2,047 

1,820 

1,917 

2,307 

2,470 

3,055 

2,827 

3,347 

2,250 
1,625 

2,502 
1,397 

1,755 


1,852 


1,885 
1,495 


11,202  '     5,946 
2,015  ;     7,279 

1,862  '.     7,0S4 


2,080  '    7,929 
2,177       7,507 


2,307        8,286 


2,210       9,555 

2,405      10.431 

2,535  !     9,172 
1,300 


IS. 


11.55 


1,203 

1,690 

975 


-$5.55 

-  9.30 

-  6.63 


+  2.25 


+  6.97 
+30.35 


12. 

6.00  I  +18.37 


i  Injured  by  cold  water  flowing  directly  onto  plat.    Not  included  in  averages. 
16845°— 14 2 


10 

Result 8  of  applying  fertilizers  to  spring  crop  only — Continued. 

1911— SERIES  A. 


Plat. 


Fertilizer. 


Yield  per  acre. 


Spring  crop. 


Straw. 


Paddy 


Fall  crop. 


Straw. 


Paddy 


Total 
yield 
per  an- 
num. 


In- 
crease 

in 
paddy 
per  an- 
num. 


Cost 
of  fer- 
tilizer. 


Profit 

(+)0T 

loss 
(-)per 

an- 
num. 


None 

Superphosphate,  225  pounds; 
potassium  sulphate,  120 
pounds 

Ammonium  sulphate,  150 
pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds 

None 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  300 
pounds;  superphosphate, 
450  pounds;  potassium  sul- 
phate, 240  pounds 

Ammonium  sulphate,  300 
pounds 

Ammonium  sulphate,  150 
pounds 

None 


Lbs. 
1,430 


1,267 
1,852 


1,917 
1,202 


2,147 


3,085 
2,957 


2,535 
1,560 


Lbs. 
1,332 


1,527 
2,112 


2,372 
1,365 


2,470 

3,510 

3,380 

2,730 
1,690 


Lbs. 
1,300 


1,300 
1,202 


1,202 
1,267 


1,267 

1,300 

1,527 

1,657 
1,397 


Lbs. 
1,592 


1,690 
1,527 


1,625 
1.690 


1,755 

2,080 

2,242 
1,755 


Lbs. 
5,654 


5,784 
6,693 


7,116 
5,524 


7,574 

9,650 

9,944 

9,164 
6,402 


Lbs. 


76 


856 


1,019 

2,124 
2,319 
1,831 


$5.55 
9.30 
8.25 


11.55 

23.10 
12.00 
6.00 


-$3.65 
+  3.15 
+13.15 


+  13.92 

+30.00 
+45.97 
+39.77 


1912— SERIES  A. 


10 


None 

Superphosphate,  225  pounds; 
potassium  sulphate,  120 
pounds , 

Ammonium  sulphate,  150 
pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds 

None 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  300 
pounds;  superphosphate, 
450  pounds:  potassium  sul- 
phate, 240  pounds 

Ammonium  sulphate,  300 
pounds 

Ammonium  sulphate,  150 
pounds 

None 


1,430 
1,490 
2,345 


2,795 
1,430 


2,470 

3,705 
4,420 

3,315 

1,885 


l  1, 495 
1,690 
2,567 


2,66.5 
1,852 


2,405 

3,445 

4,095 

3,315 
2,145 


2,925 
3,180 
4,912 


5,460 
3,282 


4,875 

7,150 

8,515 

6,630 
4,030 


0 
569 
667 


407 

1,447 
2,097 
1,317 


$5.55 
9.30 
8.25 


11.55 

23.10 
12.00 
6.00 


-$5.55 
4.92 

8.42 


-  1.38 

13.07 
40.42 
26.92 


i  Injured  by  cold  water  flowing  directly  onto  plat.    Not  included  in  averages. 


11 

Kexults  of  applying  fertilizers  to  both  spring  and  fall  crops, 

1909— SERIES  B. 


Plat. 


Fertilizer. 


Yield  per  acre. 


Spring  crop. 


Straw.    Paddy.  Straw.    Paddy 


Fall  crop. 


In- 

crease 

Total  !  paddv 
yield     per  aii- 
per  an-     num 
num. 


Cost 
of  fer- 
tilizer. 


Profit 

(  +  )or 

loss 

(-)per 


None 

Superphosphate,  225  pounds; 
potassium  sulphate,  120 
pounds 

Ammonium  sulphate,  150 
pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds 

None 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  300 
pounds;  superphosphate, 
450  pounds;  potassium  sul- 
phate, 240  pounds 

Ammonium  sulphate,  300 
pounds 

Ammonium  sulphate,  150 
pounds 

None 


Lbs. 
1,300 


1,041 
1,722 


2,112 
1,267 


1,950 

2,762 

2,405 

1,950 
1,379 


Lbs. 
1,402 


1,625 
2,007 


2,128 
1,543 


2,242 

2,957 

2,730 

2,285 
1,528 


Lbs. 
2,242 


2,450 
2,450 


3,185 
2,340 


3,770 

3,542 

3,575 

3,250 
2.210 


Lbs. 
2,015 

3,2S2 

3,867 

4,582 
3,575 

4,582 

6,070 

5,200 

4,940 
3,055 


Lbs. 
7,019 


8,998 
10,046 


12,007 
8,725 


12,544 


14,331 
13,910 


12,425 
8,172 


Lbs. 


57 
1,024 


$11.10 
18.60 


1,850       16.50 


1,974 

3,177 
3,080 
2,375 


23.10 

46.20 
24.00 
12.00 


-$9. 68 
+  7.00 
+30.00 


+26.25 

+33.22 
+53.00 
+47.37 


1910-SERIES  B. 


None 

Superphosphate,  225  pounds; 
potassium  sulphate,  120 
pounds 

Ammonium  sulphate,  150 
pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds 

None 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  300 
pounds;  superphosphate, 
450  pounds;  potassium,  sul- 
phate, 240  pounds 

Ammonium  sulphate,  300 
pounds  

Ammonium  sulphate,  150 
pounds 

None 


1,722 
1,755 
2,632 


2,405 
1.755 


2,307 

3,055 

3,185 

2,470 
1,722 


U,495 
1,430 
2,860 


2,860 
2,080 


2,892 


3,705 
3,900 


2,827 
U,690 


1,560 
2,145 
2,405 


2,470 
2,145 


2,665 

3,250 

3,055 

2,967 
1,495 


il,495 
2,470 
3,055 


3,445 
2,702 


3,835 

4,267 

4,322 

3,867 
12,015 


6,272 
7,800 
10,952 


11,180 
8,742 


11,699 

14,277 

14, 402 

12, 131 
6,922 


0 
1,073 
1,463 


1,885 

3,130 
3,380 
1,852 


$11. 10 
18.60 
16.50 


23.10 

46.20 
24.00 
12.00 


-$11.10 
+     8.22 

+  20.07 


+  24.02 

+  32.05 
+  60.50 
+  34.30 


1  Injured  by  cold  water  flowing  directly  onto  plat.     Not  included  in  averages. 


12 

Results  of  applying  fertilizers  to  both  spring  and  fall  crops — Continued. 

1911— 6ERIES  B. 


Plat 


Fertilizer. 


Yield  per  acre. 


Spring  crop. 


Straw. 


Paddy, 


Fall  crop. 


Straw. 


Paddy. 


Total 
yield 
per  an- 
num. 


In- 
crease 

in 
paddy 
per  an- 
num. 


Cost 
of  fer- 
tilizer. 


Profit 
(+)or 
loss 
(-)per 
an- 
num. 


10 


None 

Superphosphate,  225  pounds; 
potassium  sulphate,  120 
pounds 

Ammonium  sulphate,  150 
pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds _ 

None 

Ammonium  sulphate,  150 
pounds;  superphosphate, 
225  pounds;  potassium  sul- 
phate, 120  pounds 

Ammonium  sulphate,  300 
pounds;  superphosphate, 
450  pounds:  potassium  sul- 
phate, 240  pounds 

Ammonium  sulphate,  300 
pounds , 

Ammonium  sulphate,  150 
pounds 

None ,. 


Lbs. 

1,625 


1,307 
2,307 


2,502 
1,332 


2,600 


3,835 

3,900 

2,535 
1,430 


Lbs. 
1910 


1,397 
2,502 


2,600 
1,627 


*  055 

4,485 

4,420 

3,152 
1,820 


Lbs. 
1,755 


1,787 

2,242 

2,405 
1,675 

2,600 

3,347 

3,185 

2,665 
1,365 


Lbs. 

12,535 


2,470 
3,022 


3,445 
2, 437 


3,737 

4,647 

4,615 

3,900 
1,917 


Lbs. 
6,  825 


7,051 
10,073 


10.952 
6,953 


11,992 

16,314 

16, 120 

12,252 
6,532 


Lbs. 


15 

1,672 
2,193 


2,940 

5,280 
5,183 
3,200 


511.10 
18.60 
16.50 


-$10.73 
+  23.20 
+  38.32 


23.10 

46.20 
24.00 
12.00 


+  50.40 

+  85.80 
+105.57 
+  68.00 


1912— SERIES  B. 


1 

None 

1,430 

1,495 

2,730 

3,055 
1,560 

3>120 

5,330 

4,680 

4,877 
Lo«t. 

1,755 

1,885 

2,665 

2,990 
2,047 

2,925 

4,322 

4,095 

3,120 
2,145 

3,185 

3,380 

5,495 

6,045 
3,607 

6,045 

9,652 
8,775 
7,995 

2 

Superphosphate,  225  pounds; 
potassium     sulphate,     120 

0 

683 

1,008 

$5.55 
9.30 
8.25 

-45.55 

3 

Ammonium     sulphate,     150 
pounds:     potassium     sul- 
phate, 120  pounds 

7.77 

4 

Ammonium     sulphate,     150 
pounds;     superphosphate, 
225  pounds 

16.95 

5 

None 

6 

Ammonium     sulphate,     150 
pounds-     superphosphate, 
225  pounds;  potassium  sul- 
phate, 120  pounds 

........ 

943 

2,340 
2,113 
1,138 

11.55 

23.10 
12.00 
6.00 

12.02 

7 

Ammonium     sulphate,     300 
pounds;     superphosphate, 
450  pounds;  potassium  sul- 
phate, 240  pounds 

Ammonium     sulphate,     300 
pounds 

35.40 

8 

40.82 

9 

Ammonium     sulphate,     150 
pounds .... 

22.45 

10 

None 

Injured  by  cold  water  flowing  directly  onto  plat.    Not  included  in  averages. 


13 


Summary  of  the  results  of  applying  fertilizer*  to  seven  crops  of  rice. 


Plat. 


Fertilizer  per  crop. 


None 

Superphosphate,  225 
pounds;  potassium 
sulphate,  120 
pounds 

Ammonium  sulphate, 
150  pounds;  potas- 
sium sulphate,  120 
pounds 

Ammonium  sulphate, 
150  pounds;  super- 
phosphate,  225 
pounds 

None 

Ammonium  sulphate, 
150  pounds;  super- 
phosphate,  225 
pounds;  potassium 
sulphate,  120 
pounds 

Ammonium  sulphate, 
300  pounds;  super- 
phosphate,  450 
pounds;  potassium 
sulphate,  240 
pounds 

Ammonium  sulphate, 
300  pounds 

Ammonium  sulphate, 
150  pounds 

None 


Series  A— one  application 
annually. 


Paddy. 


Total. 


Pounds. 
110,560 


13,519 


14,419 


16,134 
13,857 


16, 668 


20,084 
21,352 


19,476 
13,130 


In- 


Pounds 


26 


2,641 


3,175 


6,591 
7,859 
5,983 


Total 
cost  of 
fertili- 
zer. 


§22.20 


37.20 


33.00 


46.20 


92.40 
48.00 
24.00 


Total 
profit 
or  loss. 


— $21.55 


14.05 


33.02 


33.17 


72.37 
148.47 
125.57 


Series  B— two  applications  annually. 


Paddy. 


Total. 


Pounds. 
Ul,567 


14,559 


19,978 


In- 
crease. 


Pounds 


4,908 


22,050       6,) 
15,971  


23,268 


29,453 
29,282 


24,091 
14, 170 


8,198 


14,383 
14,212 
9,021 


Total 
cost  of 

fertili- 
zer. 


S38.80 


65.10 


57.75 


80.85 


161.70 
84.00 
42.00 


Total 
profit 
or  loss. 


138.  so 


57.60 


116.75 


124. 10 


197. 87 
271.30 
183.52 


Aver- 
age 

profit 

(+)or 

loss  (— ) 

per 

acre. 


-15.14 


+  9.39 


+  16. 


4-17.73 


+28.27 
+38.76 
+26.22 


3  Injured  by  cold  water  flowing  directly  onto  plat.    Not  included  in  averages. 

The  results  of  these  experiments  justify  the  conclusion  that  for 
the  present  at  least  this  soil  is  in  need  of  nitrogen  only.  Little  or  no 
effects  were  produced  in  any  case  from  the  use  of  superphosphate 
or  potassium  sulphate,  either  when  applied  with  or  without  am- 
monium sulphate.  It  is  the  custom  of  the  rice  growers  to  apply  fer- 
tilizer, when  used  at  all,  to  the  spring  crop  only,  believing  that  the 
more  unfavorable  weather  conditions  at  that  time  necessitate  the  use 
of  stimulants,  whereas  under  the  more  favorable  conditions  that  pre- 
vail during  the  late  summer  and  early  fall  fertilizers  are  less  needed. 
Moreover,  it  has  been  considered  that  the  residual  effect  resulting  from 
the  spring  application  makes  itself  felt  in  the  fall  crop.  The  above 
experiments  prove  conclusively  that  neither  of  these  opinions  is 
justified.  The  growth  of  the  fall  crop,  when  more  favorable  weather 
prevailed — i.  e.,  higher  temperature  and  longer  days — was  affected  to 
approximately  as  great  extent  by  ammonium  sulphate  as  was  that 
of  the  spring  crop.  On  the  whole  there  appeared  no  evidence  of  a 
cumulative  effect  even  from  the  heaviest  application  when  made  twice 
annually. 


14 

From  the  data  showing  the  profit  and  loss  it  is  noteworthy  that  the 
application  of  300  pounds  of  ammonium  sulphate  proved  the  most 
economical,  either  when  applied  to  the  spring  crop  only  or  to  both 
spring  and  fall  crops,  and  that  in  the  latter  case  the  profits  were  very 
large.  So  far  as  these  experiments  go,  they  show  in  addition  that  the 
yields  can  be  maintained  at  a  high  point  and  good  profit  be  made 
under  the  system  now  employed,  provided  the  proper  fertilizer  be 
used.  This  is  not  to  be  interpreted,  however,  as  being  a  recommenda- 
tion of  the  system  now  in  use,  since  it  has  been  shown  (p.  19)  that 
with  the  rotation  of  crops,  involving  the  plowing  under  of  a  legume, 
still  greater  yields  can  be  obtained.  The  rotation  system  is  far  more 
rational  and  permanent  and  ought  to  be  employed  on  all  rice  lands. 

It  has  been  found  in  other  countries  that  the  continued  application 
of  ammonium  sulphate  tends  to  produce  acidity  in  the  soil  due  to  the 
fact  that  the  sulphate  ion  tends  to  accumulate  in  the  soil.  The  oc- 
casional application  of  lime,  however,  will  correct  this  defect.  The 
highly  basic  character  of  Hawaiian  soils,  on  the  other  hand,  partic- 
ularly the  rice  soils,  justifies  the  belief  that  the  production  of  acidity 
from  the  use  of  ammonium  sulphate  will  be  far  removed  in  point  of 
time.  It  is  of  interest  in  this  connection  that  the  annual  application 
for  over  60  years  of  300  pounds  of  ammonium  sulphate  per  acre  at 
Eothamsted  to  a  soil  containing  considerable  amounts  of  calcium 
carbonate  (probably  100  tons  per  acre  in  the  first  7  inches)  has  not 
produced  injurious  acidity.  The  soil  on  which  the  above  rice  ex- 
periments were  conducted  contains  a  relatively  high  percentage  of 
lime  and  magnesia,  particularly  the  latter,  but  neither  of  these  is 
present  as  carbonate  in  more  than  very  limited  amounts.  The  carbon 
dioxid  content  of  the  soil  is  low,  not  more  than  0.10  per  cent.  The 
iron  and  aluminum,  however,  occur  largely  as  hydrates  which  give  to 
the  soil  its  basic  character,  and  which  we  may  reasonably  believe  will 
prevent  the  accumulation  of  injurious  acidity.  It  is  of  further 
interest  to  note  that  the  application  of  lime  has  been  shown  to  cause 
a  decrease  in  the  yields  of  rice  on  this  soil. 

It  would  not  be  safe,  however,  to  recommend  ammonium  sulphate 
as  the  only  fertilizer  to  be  applied  to  the  rice  lands  of  the  islands 
generally,  since  the  effects  of  fertilizers  frequently  vary  widely  on 
different  soils.  In  order  to  throw  further  light  on  this  question  some 
experiments  have  been  conducted  cooperatively  on  other  rice  lands, 
which  resulted  in  showing  that  ammonium  sulphate  produced  practi- 
cally as  large  increases  as  a  complete  fertilizer.  At  Kailua,  for 
instance,  approximately  60  per  cent  increase  in  yield  was  produced 
both  by  150  pounds  of  ammonium  sulphate  and  by  a  complete  fer- 
tilizer containing  an  equal  amount  of  ammonium  sulphate. 

As  already  pointed  out,  the  rice  soils,  as  a  rule,  are  rich  in  phos- 
phoric acid  but  contain  relatively  small  amounts  of  potash.  While 
it  is  true  that  rice  takes  up  a  large  amount  of  potash  only  a  compara- 


15 

tively  small  part  of  it  enters  the  grain.  In  addition,  only  a  compara- 
tively small  portion  of  the  stnnv  is  really  removed  from  the  land, 
it  being  the  practice  to  leave  about  one-half  of  it  on  the  ground  at  the 
time  of  harvesting,  while  the  remaining  portion  is  used  for  bedding, 
etc.,  a  large  part  of  which  sooner  or  later  is  returned  to  the  soil. 
Furthermore,  whenever  manure  is  accessible  the  Chinese  rice  growers 
cart  large  quantities  of  it  onto  the  lands,  thus  considerably  aug- 
menting the  potash  supply.  In  view  of  these  facts,  then,  it  is  hardly 
to  be  supposed  that  potash  fertilizer  will  be  required  for  many  years. 
In  the  main,  therefore,  nitrogen  fertilizers  only  are  recommended  for 
Hawaiian  rice  lands. 

In  this  connection  the  question  of  the  form  of  nitrogen  best  suited 
to  rice  naturally  arises.  Experimental  data  have  been  obtained  on 
this  subject  which  permit  the  drawing  of  definite  conclusions. 

THE  FORM  OF   NITROGEN  FOR  RICE. 

One  of  the  most  generally  accepted  teachings  in  all  agricultural  lit- 
erature, based,  however,  mainly  upon  experiments  with  dry-land 
crops,  is  that  of  the  high  availability  of  nitrates,  it  being  considered 
that  of  all  the  forms  of  nitrogen  nitrate  is  the  most  readily  taken  up 
from  the  soil  and  used  as  food  by  plants.  As  a  result  of  the  preva- 
lence of  this  view  nitrates  have  been  used  for  rice  in  America,  and 
indeed  sodium  nitrate  still  is  recommended  at  the  present  time  for 
this  crop  by  some  authorities. 

It  has  been  known  in  oriental  countries  for  soma  time,  however, 
that  nitrate  is  not  the  most  profitable  form  of  nitrogen  to  apply  to 
rice.  Xagaoka,1  in  Japan,  demonstrated  in  1905  the  superiority  of 
ammonium  sulphate  in  a  series  of  pot  experiments.  He  found  that 
while  the  effects  produced  by  nitrates  were  variable  and  discordant 
the  yields  were  greatly  increased  in  every  instance  by  the  use  of  am- 
monium sulphate.  As  a  result  of  his  experiments  Nagaoka  concluded 
that  the  value  of  ammonium  sulphate  and  nitrates  stand  in  the  ratio 
of  100  to  10. 

In  1907  Daikuhara  and  Imaseki 2  also  found  ammonium  sulphate 
to  be  much  more  effective  for  wet-land  rice  than  either  sodium  nitrate 
alone  or  a  combination  of  the  two  forms.  The  value  of  nitrate  was 
also  found  to  be  considerably  less  when  applied  in  conjunction  with 
organic  manures.  Likewise  it  has  been  shown  in  several  of  the  Prov- 
inces of  India  that  other  forms  are  superior  to  nitrates.  Coleman 
and  Ramachandra  Rao,3  for  example,  pointed  out  that  organic  fer- 
tilizers produced  a  marked  stimulation  of  the  growth  of  rice  in 
Mysore,  while  niter  had  but  little  effect.     In  1911  the  writer  4  pub- 

1  Bui.  Col.  Agr.,  Tokyo  Imp.  T'niv.,  G   (1904),  pp.  2S5-334. 
■BuL  Imp.  Cent.  Agr.  Expt.  Sta.  Japan,  1    (1907),  No.  2,  pp.  7-36. 
•Dept.  Agr.  Mysore,  G^n.  Ser.  Bui.  No.  2,   1912. 
4  Hawaii  Sta.  Bui.  24. 


16 

lished  the  results  of  experiments  conducted  at  the  Hawaii  station 
which  showed  the  great  superiority  of  ammonium  sulphate  over 
different  nitrates. 

Notwithstanding  these  facts  some  American  writers  continue  to 
recommend  sodium  nitrate  for  rice  and  to  discuss  rice  soils  from  the 
same  standpoint  as  dry  lands. 

It  is  not  necessary  to  go  into  a  theoretical  discussion  of  this  ques- 
tion at  this  time  further  than  to  state  that  abundant  experimental 
evidence  has  already  been  brought  forth  in  various  parts  of  the 
world  to  prove  that  nitrate  is  not  the  only  form  of  nitrogen  available 
to  plants.  Results  obtained  at  the  Hawaii  station  show  that  nitrate 
can  hardly  be  considered  to  be  the  principal  source  of  combined 
nitrogen  for  many  plants  when  grown  in  the  state  of  nature.  It  is 
known  that  nitrates  are  ill  suited  to  assimilation  by  rice. 

To  study  the  practical  effects  produced  on  the  growth  of  rice  by 
ammonium  sulphate  and  nitrate  nitrogen,  respectively,  a  series  of 
plats  was  arranged  alongside  of  those  used  in  the  experiments  dis- 
cussed above.  To  one  plat  ammonium  sulphate  and  to  another  nitrate 
of  soda  was  applied  before  the  time  of  planting.  To  other  plats 
ammonium  sulphate  and  sodium  nitrate  were  applied  in  smaller 
quantities,  the  same  being  repeated  at  intervals  of  10  days  until 
six  applications  had  been  made.  To  each  plat  the  total  amount  of 
nitrogen  applied  per  acre  was  the  same,  and  the  experiments  were 
repeated  for  three  successive  crops.    The  results  follow: 

Comparison  of  ammonium  sulphate  and  sodium  nitrate  on  rice. 


Nitrogen  applied. 

Fall  crop,  1909. 

Spring  crop,  1910. 

Fall  crop.  1910. 

Straw. 

Paddy. 

Total. 

Straw. 

Paddy. 

Total. 

Straw. 

Paddy. 

Total. 

Ammonium   sulphate    (ap- 
plied before  planting) 

Sodium  nitrate  (applied  be- 

Lbs. 

3,168 

1,881 
2,475 

2,277 

Lbs. 

4,603 

2,475 
3,465 
2,623 

Lbs. 
7,771 

4,356 

5,940 

4,900 

Lbs. 

3,316 

2,029 

2,772 

1,633 
1,930 

Lbs. 

3,564 

2,128 

3,078 

2.079 
2,178 

Lbs. 

6,880 

4, 157 

5,850 

3,712 
4,108 

Lbs. 

2,920 

2,227 

2,722 

1,831 
2, 145 

Lbs. 
4,010 

3,312 

3,762 

2, 427 ' 
2, 762 

Lbs. 
6,930 

5,539 

6,484 

4,258 

Ammonium    sulphate    (ap- 
plied in  six  applications) . . . 
Sodium  nitrate  (applied  in 

Check 

4.907 

From  the  above  yields  it  is  -apparent  that  nitrate  of  soda  pro- 
duced only  slight  increases  either  when  applied  before  transplanting 
or  at  intervals  during  the  growth  of  the  crop.  Ammonium  sulphate, 
on  the  other  hand,  brought  about  notable  increases  in  every  instance, 
the  larger  harvests  having  been  obtained  from  the  single  application 
before  planting.  The  repeated  applications  were  made  for  the  pur- 
pose of  guarding  against  the  loss  of  nitrate  through  leaching,  but 
this  appeared  to  have  no  advantage  over  the  single  application. 


17 

From  pot  experiments,  where  drainage  was  entirely  prevented,  the 
great  superiority  of  ammonium  nitrogen  over  nitrate  was  again  dem- 
onstrated. In  a  series  of  pot  experiments  with  the  use  of  sterile 
quartz  sand,  it  was  found  that  where  nitrate  was  the  only  form  of 
combined  nitrogen  present  rice  made  very  poor  growth,  whereas 
ammonium  forms  seemed  to  be  well  suited  to  its  needs.  The  net 
result  of  all  these  experiments  forces  the  conclusion  that  nitrate  is 
not  a  suitable  form  of  nitrogen  for  rice,  but  that  ammonium  com- 
pounds are  well  adapted  to  its  needs.1 

In  the  rice-producing  countries  of  the  Orient  organic  manures  are 
the  chief  source  of  nitrogen  applied  to  rice  soils.  It  has  long  been 
the  custom  of  the  Chinese  and  Japanese  to  grow  some  legume  between 
crop>  for  the  purpose  of  enriching  the  soil.  Sometimes  the  legume 
is  grown  on  one  field,  cut,  and  then  distributed  over  others,  so  as  to 
gain  the  benefit  of  green  manuring  with  as  little  interruption  in  the 
growing  of  rice  as  possible.  In  addition,  all  sorts  of  organic  nitroge- 
nous substances  are  freely  applied.  In  Hawaii,  on  the  other  hand, 
almost  no  rotation  is  practiced. 

From  a  single  experiment  conducted  by  the  agronomist  of  this 
station,  however,  it  was  found  that  by  plowing  under  a  few  months' 
growth  of  alfalfa  just  previous  to  the  planting  of  rice  the  yield  was 
50  per  cent  greater  than  has  ever  been  obtained  on  this  soil  by  the 
application  of  any  commercial  fertilizer.  In  this  experiment  the 
alfalfa  was  grown  on  one  plat,  but  was  cut  and  applied  to  another, 
so  that  the  effects  may  be  attributed  to  the  organic  manure  directly 
rather  than  to  a  combination  of  aeration  and  other  effects,  the  soil 
being  prepared  and  submerged  very  soon  after  making  the  applica- 
tion. Moreover,  the  application  of  different  organic  nitrogenous 
fertilizers  at  various  times  has  always  resulted  in  substantial  in- 
creases in  the  yield  of  rice  on  this  soil.  In  a  series  of  pot  experi- 
ments, for  example,  soy-bean  cake  was  compared  with  ammonium 
sulphate.  In  this  experiment  nitrogen  from  each  of  the  two  sources 
was  applied  at  the  rate  of  70  pounds  per  acre.  The  yield>  obtained 
were  as  follows: 


Ammonium 

sulphate  versus  soy-bean  cake  < 

.v  fertilizers  foi 

rice. 

ment  of  plat. 

Straw. 

Paddy. 

Total. 

Grams. 
215 
107 

80 

Grams. 
13fl 
122 
01 

Grams. 
353 

Check        

141 

From   the   above  data    it    will    be  seen   that    soy-bean   cake   brought 

about  an  increase  of  100  per  cent  in  the  yield,  but  was  considerably 
inferior  in  this  respect  to  ammonium  sulphate.    The  reasons  for  the 

1  The   full    data    with    reference   to    the   assimilation   of   different   forms   of   nitrogen    by 
rice  and  a  more  complete  bibliography  of  this  subject  will  be  found  in  Hawaii  Sta.  Bui.  24. 


18 


superiority  of  ammonium  sulphate  over  organic  forms  of  nitrogen 
are  discussed  in  greater  detail  on  page  21.  In  this  connection  it  is 
of  interest  to  point  out  that  the  plant  absorbs  the  principal  part  of 
its  nitrogen  during  the  early  period  of  its  growth ; 1  readily  available 
nitrogen  therefore  is'  needed  when  the  rice  is  young,  and  since  the 
production  of  available  nitrogen  from  organic  forms  requires  consid- 
erable time  the  application  should  be  made  some  time  in  advance  of 
planting,  a  precaution  that  was  not  taken  in  the  above  experiments. 
Through  a  period  of  years,  however,  the  total  effects  would  probably 
become  more  nearly  equal. 

AMMONIFICATION  AND  NITRIFICATION  IN  RICE  SOILS. 

The  analysis  of  a  number  of  rice  soils  taken  from  the  field  when 
wet  and  analyzed  immediately  has  shown  that  rice  soils  contain  con- 
siderable quantities  of  ammonia,  varying  from  a  few  parts  up  to  as 
much  as  50  or  60  parts  per  million.2  On  the  other  hand,  in  the  sub- 
merged condition  nitrate  is  rarely  found  in  more  than  mere  traces, 
frequently  being  entirely  absent. 

Since  good  effects  are  known  to  follow  the  use  of  organic  manures, 
and,  furthermore,  that  ammoniacal  nitrogen  is  especially  effective 
with  rice,  it  becomes  a  matter  of  interest  to  ascertain  whether  or  not 
ammonia  is  formed  in  rice  soils  at  rates  sufficient  to  supply  the  needs 
of  rice. 

Accordingly  a  series  of  ammonification  experiments  were  carried 
out  with  dried  blood  as  the  source  of  nitrogen,  using  varying  amounts 
of  water,  starting  in  with  the  air-dry  condition  and  increasing  the 
amounts  of  water  applied  up  to  and  beyond  the  saturation  point. 
One  hundred  gram  portions  of  soil  were  placed  in  tumblers  with  2 
grams  of  dried  blood  added  to  each.  After  an  incubation  period  of 
seven  days  the  ammonia  was  determined  by  distilling  with  mag- 
nesium oxid  into  standard  acid.  The  results  obtained  were  as  fol- 
lows : 
Influence  of  varying  amounts  of  water  on  the  ammonification   of  dried   hlood. 


Water  added. 

Nitrogen  found  as 
ammonia. 

Water  added. 

Nitrogen  found  as 
ammonia. 

Soil  292. 

Soil  461. 

Soil  292. 

Soil  461. 

Mg. 
2.2 
2.2 
37.8 

Mg. 

3.9 

5.1 

4.3 

25.5 

41.2 

53.2 

59.0 

35  cc 

Mg. 
131.1 

Mg. 

86.8 

40  cc.  . 

90.5 

<54.5 

:>n.  7 

85.4 

10  cc...          

71.2 

15  cc 

164.9 

85. 3 

20  cc 

165.5 
164.6 
140. 1 

55  cc 48.2 

65  cc 

52.4 

25  cc 

<  15.1 

30  cc 

70  cc 

16.1 

1  Hawaii  Sta.  Bui.  21. 

2  Fraps  also  showed  in   1908  that  ammonification  takes  place  much  more  vigorously 
rice  soils  of  Texas  than  does  nitrification   (Texas  Sta.  Bui.  82). 

8  Each  soil  contained  about  5  per  cent  moisture. 
4  Saturated. 


19 

It  is  here  seen  that  ammonification  proceeded  at  a  slow  rate  only, 
if  at  all.  until  a  certain  moisture  content  was  veaefaed  (about  10  per 
cent  in  the  case  of  soil  292  and  15  per  cent  with  that  of  461  >,  above 
which  vigorous  ammonification  took  place,  which  steadily  increased 
up  to  an  approximate  two-thirds  saturation,  then  decreased  as  com- 
plete saturation  was  approached.  There  was.  however,  active  am- 
monification in  the  completely  saturated  soils.  This  seem-  to  prove 
that  ammonia  is  formed  in  submerged  soils  and  that  organic  nitroge- 
nous fertilizers  will  give  rise  to  nitrogen  available  to  rice  under  con- 
ditions that  prevail  in  rice  cultures. 

As  is  well  known,  the  formation  of  ammonia  results  from  the 
activity  of  a  wide  range  of  soil  organisms,  bacteria  and  fungi,  some 
of  which  are  aerobic  and  some  anaerobic.  While  the  above  data 
show  that  ammonification  is  more  active  with  moisture  supplies 
below  the  saturation  point,  being  greatest  at  approximately  two- 
thirds  saturation ;  nevertheless,  the  fact  that  ammonification  can  take 
place  in  saturated  soils  is  of  very  great  importance  in  the  growth  of 
rice.  It  makes  possible  the  production  of  available  nitrogen  in  rice 
soils  without  the  necessity  of  employing  cultural  methods  that  are 
primarily  designed  to  bring  about  aerated  conditions. 

Free  oxygen  being  essential  to  nitrification,  it  seems  justifiable  to 
conclude  that  nitrification  does  not  take  place  to  any  considerable 
extent  in  a  submerged  soil.  In  order  to  throw  positive  light  on  the 
question,  however,  search  was  made  for  nitrates  in  various  submerged 
soils  about  Honolulu,  but  in  no  instance  was  more  than  a  few  parts 
per  million  found.  In  some  laboratory  experiments  it  was  further 
found  that  practically  no  nitrification  took  place  in  submerged  soils. 

The  process  of  denitrification,  however,  is  of  considerable  impor- 
tance in  this  connection.  As  is  well  known,  free  nitrogen  gas  may 
be  one  of  the  products  of  the  decay  of  organic  manures.  Likewise, 
it  is  also  known  that  certain  denitrifying  bacteria  break  down  nitrates 
into  nitrites,  ammonia,  and  finally  into  free  nitrogen  gas.  The  con- 
ditions under  which  the  denitrifying  bacteria  function  are  extremely 
varied,  but  the  two  conditions  most  favorable  for  their  activity  are  a 
source  of  food  supply  and  a  lack  of  free  oxygen.  In  the  rice  soils  of 
Hawaii  these  conditions  are  abundantly  met;  tfre  high  content  of 
organic  matter  guarantees  a  source  of  food,  while  supersaturation 
excludes  the  air. 

A-  indicated  above,  the  denitrification  processes  may  be  conven- 
iently divided  into  two  classes,  (1)  those  causing  a  liberation  of 
nitrogen  from  organic  materials,  and  (2)  those  bringing  about  a 
reduction  in  the  nitrates  present.  The  latter  of  these  has  been  the 
subject  of  considerable  study  at  the  Hawaii  station. 


20 

In  pot  experiments  conducted  some  time  ago  for  the  purpose  of 
studying  the  nutritive  value  of  different  forms  of  nitrogen  it  was 
found  that  in  every  instance  the  addition  of  nitrate  to  submerged 
soil  resulted  in  the  formation  of  comparatively  large  amounts  of 
nitrite  within  a  few  days  after  the  time  of  application.  In  sand  cul- 
tures similar  effects  were  observed  except  where  complete  steriliza- 
tion was  effected.  Furthermore,  wherever  any  considerable  amount 
of  nitrite  was  formed,  more  than  5  to  6  parts  per  million,  toxic  effects 
were  produced,  while  still  greater  amounts  caused  the  rice  to  turn 
yellow  and  later  to  die. 

Nitrite,  however,  was  not  produced  to  any  considerable  extent 
when  organic  ammoniacal  nitrogen  was  the  only  form  of  combined 
nitrogen  present,  A  further  objection  to  the  use  of  nitrates  as  fer- 
tilizer for  rice  is  found  in  the  fact,  therefore,  that  nitrates  become 
reduced  to  nitrites,  which  are  extremely  poisonous  to  rice.  Nitrate, 
then,  is  unsuited  to  the  nutrition  of  rice,  and  in  turn  may  give  rise 
to  a  substance  that  is  distinctly  poisonous. 

THE  MANAGEMENT  OF  RICE  SOILS. 

During  the  past  few  years  an  increasing  amount  of  study  has  been 
given  to  the  question  of  soil  management  and  cultural  methods,  the 
rotation  of  crops,  and  various  methods  of  soil  treatment  are  coming 
to  be  viewed  in  their  relation  to  this  general  question.  Investiga- 
tions on  special  phases  of  this  subject  have  thrown  new  light  on  the 
important  question  of  soil  fertility  in  general  and  on  that  of  sub- 
merged soils  in  particular. 

In  an  investigation  on  the  solubility  of  the  island  soils1  some 
data  of  interest  in  this  connection  were  recently  obtained.  Likewise 
Coleman  and  Ramachandra  Rao2  studied  the  effects  on  the  yield  of 
rice  of  aerating  the  soil. 

The  solubility  of  substances  in  submerged  soils  has  been  found  to 
be  abnormally  high,  the  amounts  of  the  several  mineral  constituents 
going  into  solution  in  water  having  been  found  to  be  considerably 
greater  than  were  obtained  from  any  of  the  dry-land  soils  of  the 
islands.1  After  the  wet  soil  was  allowed  to  thoroughly  dry  out, 
however,  the  solubility  in  water  was  found  to  be  greatly  decreased, 
falling  to  about  the  same  degree  as  that  of  dry  lands.  Similar  data 
have  also  been  obtained  by  Coleman  and  Ramachandra  Rao,  in 
Mysore.2  This  seems  referable  in  the  main  to  soil  colloids  and  the 
formation  of  soil  films  in  the  air-dried  state.  The  overcoming  of 
film  pressure  and  diffusion  of  dissolved  materials  upon  resubmerg- 
ence  require  considerable  time,  so  that  the  amount  of  soluble  plant 

1  Hawaii  Sta.  Bui.  30. 

2  Dcpt.  Agr.  Mysore,   Gen.   Ser.   Bui.  No.  2,   1012. 


21 

food  coming  into  contact  with  the  absorbing  root  surfaces  of  rice 
would  be  considerably  less  when  planted  in  a  soil  thai  had  been 
thoroughly  dried  out.  Later  the  mineral  constituents  would,  of 
course,  regain  their  former  state  of  solubility,  but  just  how  much 
time  would  be  required  for  the  reestablishment  of  a  permanent  con- 
centration can  not  be  definitely  stated.  It  seem-  certain,  however, 
that  a  lowering  of  the  availability  of  the  mineral  constituents  would 
temporarily  result  from  a  thorough  drying  out  of  the  soil. 

It  is  now  the  practice  of  the  growers,  both  on  the  mainland  and  in 
Hawaii,  to  plow  their  rice  lands  some  weeks  before  the  flooding  time, 
in  the  latter  case  immediately  following  each  harvest,  so  as  to  permit 
as  much  aeration  of  the  soil  as  possible.  As  would  be  expected  the 
aeration  prevents  nitrification,  so  that  by  the  time  a  new  crop  is 
planted  nitrate  has  accumulated  to  a  considerable  extent.  Upon 
resubmergence  the  nitrate  thus  formed  becomes  partially  leached  out 
of  the  soil  and  in  part  converted  into  poisonous  nitrites.  The  nitri- 
fication therefore  leads  to  a  direct  loss  of  nitrogen  on  the  one  hand 
and  to  the  formation  of  a  substance  toxic  to  rice  on  the  other.  If, 
however,  Hawaiian  rice  soils  are  not  plowed  or  cultivated  after  the 
water  is  turned  off  and  the  previous  crop  harvested  little  or  no 
nitrification  sets  in.  The  puddled  state  of  the  soil  and  its  compacted 
condition  effectively  exclude  air.  It  is  only  after  cultivation  and 
consequent  aeration  that  active  nitrification  sets  in. 

Unfortunately  no  experiments  showing  the  practical  effects  on 
the  growth  of  rice  as  produced  by  aeration  against  nonaeration  have 
been  conducted  at  this  station.  Such  experiments,  however,  have 
been  made  in  Mysore,  the  results  of  which  are  in  complete  harmony 
with  the  inferences  drawn  from  the  nitrogen  transformations  above 
referred  to.  As  a  result  of  experiments  carried  on  through  two 
years,  Coleman  and  Ramaehandra  Rao  x  found  that  a  considerable 
gain  in  the  yield  of  rice  was  obtained  by  leaving  the  land  in  the 
unplowed  condition  during  the  time  between  crops,  the  plowing  for 
the  newT  crop  being  deferred  until  just  before  the  new  crop  was 
planted.  By  growing  a  legume  between  rice  crops  all  needed  aera- 
tion can  be  brought  about;  while  the  nitrates  formed  during  this 
period  would  be  absorbed  to  a  large  extent  by  the  legume,  and  in 
addition  free  nitrogen  from  the  air  would  be  added  to  the  -oil 
through  the  growth  of  the  Legume.  Upon  plowing  under  the  Legume 
ammonification  will  set  in,  thus  furnishing  available  nitrogen  for  the 
next  rice  crop.  The  nitrogen  requirements  of  the  rice  would  there- 
fore be  met  and  other  beneficial  effects  that  arc  believed  to  result 
from  the  rotation  of  crops  would  be  secured.     There  i^  little  ground 

1  LOC.    'il..    P.   \K 


22 

to  doubt  that  better  conditions  would  thus  be  established  and  greater 
profits  obtained. 

In  the  carrying  out  of  the  experiments  reported  in  this  bulletin 
assistance  has  been  rendered  by  various  members  of  the  station  staff, 
to  whom  thanks  are  hereby  extended. 

SUMMARY. 

(1)  Hawaiian  rice  soils  have  originated  from  basaltic  lava,  but 
also  contain  small  amounts  of  coral  limestone. 

(2)  In  texture  most  of  the  rice  lands  are  clay  loams,  and  contain 
approximately  equal  quantities  of  fine  sand,  silt,  fine  silt,  and  clay. 

(3)  In  chemical  composition  these  soils  are  quite  similar,  with 
the  exception  of  those  from  the  Waikiki  and  Kaulaunui  districts, 
the  former  of  which  contain  abnormal  amounts  of  magnesia,  while 
the  latter  are  highly  organic.  In  general,  the  nitrogen  and  phos- 
phoric acid  are  high,  while  the  potash  is  1owt,  due  largely  to  the 
solubility  of  potash,  which  is  leached  from  the  soil. 

(4)  From  fertilizer  experiments  carried  on  through  seven  crops  it 
was  found  that  the  application  of  150  pounds  per  acre  of  ammonium 
sulphate  produced  notable  increases  in  the  yield,  but  300  pounds  per 
acre  proved  the  more  profitable.  Potash  and  phosphoric  acid  were 
without  effect.  The  application  of  ammonium  sulphate  to  both  the 
spring  and  fall  crops  yielded  considerably  more  profit  than  when 
made  to  the  spring  crop  only.  The  residual  effects  on  the  fall  crop 
from  the  spring  application  are  small.  The  immediate  effects  ob- 
tained from  making  the  application  to  the  fall  crop  were  about  the 
same  as  those  obtained  wTith  the  spring  crop. 

(5)  A  complete  fertilizer  proved  no  more  effective  than  ammonium 
sulphate  alone,  whereas  the  application  of  both  ammonium  sul- 
phate and  potassium  sulphate  caused  a  decrease  as  compared  with 
that  obtained  from  ammonium  sulphate  alone. 

(6)  Nitrogenous  fertilizers  only  are  recommended  for  Hawaiian 
rice  soils,  and  for  immediate  effects  a  given  amount  of  nitrogen  in 
the  form  of  ammonium  sulphate  will  produce  greater  returns  than 
from  organic  sources.  Under  no  circumstances  should  nitrates  be 
used  as  fertilizer  for  rice. 

(7)  With  nitrate  as  the  only  source  of  combined  nitrogen  for  rice 
poor  growth  results.  In  addition  nitrates  in  submerged  soils  become 
reduced  to  nitrites,  wmich  are  poisonous  to  rice.  Ammoniacal  nitro- 
gen, on  the  other  hand,  is  well  suited  to  the  needs  of  rice. 

(8)  Very  little  nitrification  takes  place  in  submerged  soil;  am- 
monification,  however,  goes  on,  not  so  vigorously  as  in  aerated  soils, 
but  sufficiently  to  supply  the  nitrogen  needs  of  rice,  provided  suffi- 
cient organic  matter  is  present  in  the  soil. 


23 

(9)  A  rotation  of  crops,  including  the  plowing  under  of  a  legume, 
is  recommended.  It  is  believed  a  system  can  be  worked  out  whereby 
a  legume  can  be  grown  between  crops  and  then  plowed  under,  thus 
gaining  the  benefits  of  the  rotation  and  at  the  same  time  permitting 
the  growing  of  two  crops  of  rice  annually. 

(10)  Rice  soils  should  not  be  plowed  and  then  allowed  to  lie  fallow 
between  crops.  Nitrification  sets  in  immediately  after  aerated  con- 
ditions are  produced  and  the  nitrates  thus  formed  become  converted 
into  poisonous  nitrites  upon  resubmergence.  or  are  lost  through 
leaching.  When  no  rotation  is  practiced  it  is  better  to  leave  the  land 
unplowed  until  just  before  planting  the  next  crop. 


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